Over 600 students and staff members across multiple schools in Kumatori Town, Osaka, have reported symptoms of food poisoning, local media said on Thursday.
Students and staff at eight elementary and junior high schools in the town began developing symptoms, including diarrhoea and vomiting, about a week ago.
As of Tuesday, the total number of those affected had risen to 633, according to reports.
The local health centre detected norovirus in some of the affected students.
The same virus was also found in employees of a company that supplied bread for school lunches to all elementary and junior high schools in the town.
Based on these findings, the public health centre concluded that the outbreak stemmed from food poisoning caused by bread served during school lunches.
The health centre subsequently imposed a five-day business suspension on the bread manufacturer.
